Most computer systems include a memory storage device such as a hard disk drive for storing large amounts of data. Hard disk drives typically include a magnetic disk that stores a large amount of binary information. This magnetic disk is typically coupled to a hub that is rotated by an electric motor commonly referred to as a spin motor. In order to write information to and read information from the disk, a head is employed which magnetizes and senses the magnetic field of the disk. The head is commonly referred to as a transducer. The head is typically located at the end of a cantilevered actuator arm that pivots about a bearing assembly mounted on a base plate. The actuator arm has a coil which cooperates with a magnet mounted on the base plate. Providing current to the coil creates torque on the actuator arm and moves the head relative to the disk. The coil and magnet are commonly referred to as a voice coil motor.
The disk drive contains integrated circuits that control the operation of the drive. The circuits typically include a read/write channel that is coupled to the head and an interface controller. The interface controller is coupled to the host computer and a random access memory (RAM) buffer to store data transferred between the disk and the host computer.
Data is recorded on the disk in the form of magnetic transitions spaced closely together. In modern disk drives, recording densities both in terms of tracks per inch and linear density along a track have reached a level which creates extreme sensitivity to imperfections in the disk. These imperfections are known as media defects and occur in the magnetic recording layer of the disk. Media defects cause portions of the magnetic recording layer to be unacceptable for recording the magnetic transitions. Media defects can be small, affecting only a small number of transitions on a small number of tracks, or large, affecting many transitions across multiple tracks.
Manufacturing tests processes are performed on the disk drive at the factory prior to its installation in a computer system. These tests include flaw mapping, embedded runout compensation (ERC) and final drive verification.
Flaw mapping performs a write/verify process over the tracks to identify logical block addresses (LBAs) which possess defects and may not be able to receive and store information. The locations of LBAs with defects are stored in a flaw map. ERC corrects irregularities in the shape of the tracks (cylinders). An error value is generated which indicates the distance between the head and the center of the track at a particular location on the track. The error value provides alignment correction for the head during the read/write process for a particular track on the disk. Final drive verification is a follow-up to flaw mapping that confirms that the LBAs do not contain flaws.
Unfortunately, these manufacture test processes are very time consuming. As the number of tracks in the disk drive has increased, the total number of passes made at each location in performance of these tests has increased which in turn increases the manufacture time for the disk drive.